There are presently two methods of read only memory (ROM) implementation that use single N-channel (NCH) transistors to program a logic low or 0 on a bitline. In the first method, shown in FIG. 1, a P-channel transistor and an N-channel transistor are used to convey logic signals to a respective bitline.
Bitlines Bitline0 and Bitline1 are precharged logic high by P-channel (PCH) transistors 10 and 12, respectively. The gates of P-channel transistors 10 and 12 are connected to a clock which transmits clock signals that control the precharge mode. The drain, source and gate of N-channel transistor 14 are connected to Bitline0, ground and Row0, respectively. The drain, source and gate of N-channel transistor 16 are connected to Bitline 1, ground and Row1, respectively. A logic high or 1 at the gate of N-channel transistor 14 turns on transistor 14 effectively connecting Bitline0 to ground. The result is a logic low or 0on Bitline0. Contrariwise, a logic low or 0 at the gate of N-channel transistor 14 turns off transistor 14 disconnecting Bitline0 from ground. The result is a logic high or 1 on Bitline0. Similarly, a logic high or 1 at the gate of N-channel transistor 16 turns on transistor 16 effectively connecting Bitline 1 to ground. The result is a logic low or 0 on Bitline 1. Contrariwise, a logic low or 0 at the gate of N-channel transistor 16 turns off transistor 16 disconnecting Bitline1 from ground. The result is a logic high or 1 on Bitline1.
In the second method, shown in FIG. 2, two N-channel transistors are used to convey logic signals to a respective bitline. The drain, source and gate of N-channel transistor 18 are connected to bitline 20, ground and Row0, respectively. The drain, source and gate of N-channel transistor 22 are connected to bitline 20, ground and Row1, respectively. A logic high or 1 at the gate of N-channel transistor 18 turns on transistor 18 effectively connecting Bitline 20 to ground. The result is a logic low or 0 on Bitline 20. A logic low or 0 at the gate of N-channel transistor 18 turns off transistor 18 disconnecting Bitline 20 from ground. Similarly, a logic high or 1 at the gate of N-channel transistor 22 turns on transistor 22 effectively connecting Bitline 20 to Vcc. The result is a logic high or 1 on Bitline 20.